Properties marked with `predicate` in the schema are now accepted.
* in the dbscheme, they will translate to a table with a single `id`
column (and the table name will not be pluralized)
* in C++ classes, they will translate to `bool` fields
* in QL classes, they will translate to predicates
Closes https://github.com/github/codeql-c-team/issues/1016
This checks in the trapgen script generating trap entries in C++.
The codegen suite has been slightly reorganized, moving the templates
directory up one level and chopping everything into smaller bazel
packages. Running tests is now done via
```
bazel run //swift/codegen/test
```
With respect to the PoC, the nested `codeql::trap` namespace has been
dropped in favour of a `Trap` prefix (or suffix in case of entries)
within the `codeql` namespace. Also, generated C++ code is not checked
in in git any more, and generated during build. Finally, labels get
printed in hex in the trap file.
`TrapLabel` is for the moment only default-constructible, so only one
single label is possible. `TrapArena`, that is responsible for creating
disjoint labels will come in a later commit.
